Photolithographic pattern generation

ABSTRACT

In a method for producing photolithographic patterns in the submicron range, applied on a substrate is a photoresist layer comprised of a polymer containing carboxylic acid anhydride groups and tert. butylester or tert. butoxy-carbonyloxy groups, a photoactive component--in the form of an ester of a naphthoquinonediazide-4-sulfonic acid with an aromatic or aliphatic-aromatic hydroxy compound--and a suitable solvent; the photoresist layer is then dried, exposed in an imaging manner, and subjected to a temperature treatment in the range of between 120° and 150° C. for a duration of 100 to 600 seconds. The photoresist layer is then subjected to a liquid silylation and is dry-developed in an anisotropic oxygen plasma.

The invention relates to a method for producing photolithographicpatterns--using a dry developable single-layer resist system--in thesubmicron range.

"Chemically amplified resists" are widely used in microelectronics (see"Solid State Technology", vol. 34 (1991), no. 8, pp. 53 to 60). Thechemical amplification is performed both when working withwet-developable single-layer resists, as well as with wholly orpartially dry-developable resists. The resists are able to work inaccordance with the principle of cleavage by acid catalysis, polar, butblocked chemical groups, such as carboxyl groups or phenolic hydroxylgroups being deblocked by a photolytically produced acid, and the resistundergoing a polarity change in the exposed regions. This polaritychange can be used for a selective silylation when working withdry-developable resists, for example. Examples of blocking groups aretert. butylester and tert. butoxy-carbonyloxy groups.

Published European Patent application 0 492 256 discloses aphotolithographic pattern generation, where a dry-developable resist issubjected to a temperature treatment following irradiation (postexposure bake=PEB) and is then silylated from the liquid phase andsubsequently anisotropically etched in an oxygen plasma. Positive ornegative patterns are produced depending on the type of silylationsolution. The resist is generally comprised of at least two solidconstituents, i.e., of a base polymer and a photoactive acid former. Thebase polymer contains carboxylic acid anhydride and tert. butylesterpartial structures, the acid former is preferably an onium compound,such as diphenyliodonium- andtriphenylsulfonium-trifluoromethanesulfonate. A resist of this type isespecially suited for photopatterning in the sub-micron andsubhalf-micron range with very steep side walls. In a pattern generationcarried out in the manner described above, the so-called "delay time"effect was ascertained--in the same way as in other known resist systemswhich work according to the principle of acid-catalyzed cleavage.Namely, if the delay time between exposure and temperature treatment(PEB) exceeds a certain value, considerable discrepancies occur betweenthe nominal pattern dimension (pattern size on the mask) and the imagedpattern (pattern size in the resist following development). The longerthis delay time is, the greater the discrepancy. Above a certain valuefor the time delay, for example about 30 minutes, in the case ofanhydride group-containing resists of the type mentioned above, almostno patterns are recognizable after development. The tolerable delay timefor these resists is approximately 5 to 10 minutes. From a standpoint ofproduction engineering, however, a delay time of this kind is notacceptable.

The problem portrayed here is generally known and is attributed toalkaline contamination in the air, which deactivates the photochemicallyproduced strong acid during the delay time. It has already beenproposed, therefore, to solve this problem by filtering the air usingactivated carbon (see: "Proc. SPIE", vol. 1466 (1991), pp. 2-12).However, this requires considerable investment.

Other measures, such as admixing additives, also have not resulted in adecisive attenuation of the delay time effect (see: "Proc. SPIE", vol.1466 (1991), pp. 13-25). The delay time can, in fact, be prolonged byapplying an additional layer, but only to a minor extent. Moreover, sucha measure constitutes an additional process step, which is not desirablein a production because it leads to loss of efficiency.

The object of the invention is to disclose a method that operates on theprinciple of acid-catalyzed cleavage--for photolithographic patterngeneration, which--when working with resist systems of the typementioned at the outset--will enable the delay time problem to be solvedwithout entailing additional process steps or investments; i.e., thedelay time between irradiation and temperature treatment (of a value ofapprox. 10 minutes) to be increased to a level that is acceptable interms of production engineering.

SUMMARY OF THE INVENTION

This is achieved in accordance with the invention in that

applied on a substrate is a photoresist layer comprised of

a polymer containing carboxylic acid anhydride groups and tert.butylester or tert. butoxy-carbonyloxy groups,

a photoactive component in the form of an ester of anaphthoquinonediazide-4-sulfonic acid having a structure of ##STR1##with an aromatic or aliphatic-aromatic hydroxy compound, the residues Rsignifying--independently of one another--hydrogen, alkyl, halogenalkyl,alkoxy, phenyl, halogenphenyl, phenoxy or halogen, and a suitablesolvent;

that the photoresist layer is dried;

that the photoresist layer is exposed in an imaging manner;

that the exposed photoresist layer is subjected to a temperaturetreatment in the range of between 120° and 150° C. for a duration of 100to 600 seconds;

that the thus treated photoresist layer undergoes a liquid silylation;and

that the silylated photoresist layer is dry-developed in an anisotropicoxygen plasma.

Underlying the method according to the invention is a dry-developable,stable-in-storage, single-layer resist, i.e., a negative resist, on thebasis of a polymer, which--besides anhydride groups--possesses tert.butylester or tert. butoxy-carbonyloxy groups. The advantage of a resistof this type is that it is not only effective in the deep UV range(DUV), but in the near UV range (NUV), as well.

The photoactive component of the resist is an ester from anaphthoquinonediazide-4-sulfonic acid and a hydroxy compound.Photoactive components of this type are known per se (see: "Methods andMaterials in Microelectronic Technology", Plenum Press, New York (1984),pp. 190-193). In the case of the invention, however, the excellentpatternability of the resist containing such a photoactive component issurprising. As a rule, namely, very strong acid formers are requiredwhen working with tert. butylester base polymers in photolithographicpattern generation.

It is essential in the method according to the invention for thetemperature treatment (PEB) to take a relatively long time, namely ≧100s, i.e., between 100 and 600 seconds, and for the PEB temperature to berelatively high, namely 120°-150° C. This method results in aprolongation of the delay time of up to 16 h and more. The delay timeproblem is solved without requiring new process steps or new materialsand without necessitating new investments.

In comparison to common resists, the proportion of photoactive componentin the case of the invention is much higher. This proportion isadvantageously 20 to 40% by mass, preferably 25 to 35% by mass, relativeto the dry photoresist, i.e., the solvent-free resist composition. Thephotoactive component can also advantageously be a mixture of an esterof the mentioned type and an onium compound. Compounds of this type,also described as Crivello salts, are, for example,diphenyliodonium-trifluoromethane sulfonate (DPIT) andtriphenylsulfonium-trifluoromethane sulfonate (TPST).

Preferably 2,3,4-trihydroxybenzophenone or bisphenol A is used as ahydroxy compound in the ester of the photoactive component.

In the method according to the invention, the polymers used arepreferably-those whose carboxylic acid anhydride groups are derived frommaleic anhydride. Another compound of this type is, for example,itaconic acid anhydride. The carboxylic acid tert.-butylester groups arepreferably based on acrylic acid, methacrylic acid, vinylbenzoic acid,or cinnamic acid-tert.-butylester, and the tert.-butoxycarbonyloxygroups preferably on tert.-butoxycarbonyloxystyrene or--maleinimide.

Generally known resist solvents are suited for use as solvents. The soleimportant criterion for selecting the solvent is that both the polymercomponent as well as the photoinitiator, i.e., the photoactivecomponent, have to be dissolved. Moreover--using the known coatingmethods--faultless resist layers must be formed on the substrates, forexample on silicon wafers or on wafers coated with a bottom resist. Thesolvent is preferably methoxypropylacetate, cyclohexanon or an ethyleneglycol- or diethylene glycol-ether, if indicated in a mixture withdibenzyl ether.

An etching resistance to dry development in the oxygen plasma iseffected by means of liquid silylation with the method according to theinvention. To this end, the resist layer is treated with a polar, proticsilylation solution. As a silylating agent, generally silicon compoundsin the form of aminosilanes or aminosiloxanes are used; these compoundscan be of an oligomeric nature. The polar, protic silylation solution ispreferably an aqueous-organic solution of the silylating agent. Thesilylating agent is advantageously dissolved in mixtures of water andalcohol, in particular ethanol and/or isopropanol; besides that, forexample, pure alcoholic solutions can be used.

The invention shall be elucidated further on the basis of exemplaryembodiments. The following starting materials or reagents are used:

Base polymer

Terpolymer of cinnamic acid tert.-butylester, maleic anhydride andstilbene, prepared through radical polymerization of the three monomersin ethyl acetate with azoisobutyric acid nitrile as an initiator.

Photoactive component (1)

Triester of 2,3,4-trihydroxybenzophenone withnaphthoquinonediazide-4-sulfonic acid.

Photoactive component (2)

Diphenyliodonium-trifluoromethane sulfonate (DPIT)

Silylation solution (1)

Aqueous-alcoholic solution comprising 2 parts by weight diaminosiloxane,78 parts by weight isopropanol and 20 parts by weight of water;preferably a α,ω-aminofunctional siloxane, in particular with twoterminal aminopropyl groups and 2 to 20 silicon atoms in the chain, isused, for example the commercial product Tegomer A-Si 2120 (firmGoldschmidt).

Silylation solution (2)

Alcoholic solution comprising 1 part by weight diaminosiloxane (TegomerA-Si 2120) and 99 parts by weight ethanol.

EXAMPLE 1

A resist consisting of 9 parts by weight of base polymer, 3 parts byweight of photoactive component (1), 79.2 parts by weight ofmethoxypropylacetate and 8.8 parts by weight of dibenzyl ether isspin-coated onto a silicon wafer and dried for 90 seconds at 90° C. on aheating plate; the layer thickness of the resist is 0.52 μm. The resistis then contact-exposed through a mask with 12 mJ/cm unit MJB 3, firmKarl Suss; λ=250 nm) and baked immediately thereafter for 120 seconds at135° C. on the heating plate (PEB). The resist is subsequently treatedat room temperature and under a normal pressure, i.e., under ordinaryroom climate conditions, for 45 seconds with the silylation solution(1), and then rinsed for 30 seconds with isopropanol and subsequentlydried for 90 seconds at 90° C. on the heating plate. After drying, thewafer is placed in a plasma etching installation (type MIE 720, firmMaterial Research Corporation), and the resist is then etched with aplasma that contains oxygen (gas flow: 80 sccm) and tetrafluoromethane(gas flow: 9 sccm); the total gas pressure is 8 mTorr, the bias voltageis 40 V. Etching takes place subsequently in a pure oxygen plasma (gaspressure: 2 mTorr; bias voltage: 50 V). Negative patterns are obtainedwith vertical side walls and a line/space ratio of 1:1.

EXAMPLE 2

One proceeds as in Example 1, however, the wafer is left betweenexposure and tempering for 16 hours in an open wafer tray in the processroom. Negative patterns having vertical side walls, and a line/spaceratio of 1:1 are likewise obtained after etching. Microscopicexaminations reveal that patterns of the same nominal width on theetched wafers have the same width in Example 1 and Example 2.

EXAMPLE 3

(comparative test)

A resist consisting of 11.1 parts by weight of base polymer, 0.9 partsby weight of photoactive component (2), 79.2 parts by weight ofmethoxypropylacetate and 8.8 parts by weight of dibenzyl ether isspin-coated onto a silicon wafer and dried for 90 seconds at 90° C. on aheating plate; the layer thickness of the resist is 0.58 μm. The resistis then contact-exposed through a mask with 12 mJ/cm² (unit MJB 3, firmKarl Suss; λ=250 nm) and baked immediately thereafter for 60 s at 100°C. on the heating plate (PEB). The resist is subsequently treated atroom temperature and under a normal pressure, i.e., under ordinary roomclimate conditions, for 20 seconds with the silylation solution (2), andthen rinsed for 20 seconds with isopropanol and subsequently dried for90 seconds at 90° C. on the heating plate. After drying, the resist isetched in a plasma etching installation as in Example 1. Negativepatterns are obtained with vertical side walls and a line/space ratio of1:1.

EXAMPLE 4

(comparative test)

One proceeds as in Example 3, however, the wafer is left betweenexposure and tempering for 1 hour in an open wafer tray in the processroom. No unequivocal patterning can be ascertained following theetching, i.e., the delay time problem occurs in this case.

What is claimed is:
 1. A method for producing photolithographic patternsin the submicron range, comprising the steps of:applying onto asubstrate a photoresist layer comprisinga polymer containing carboxylicacid anhydride groups and tert. butylester or tert. butoxy-carbonyloxygroups, a photoactive component in the form of an ester of anaphthoquinonediazide-4-sulfonic acid having a structure of ##STR2##with an aromatic or aliphatic-aromatic hydroxy compound, the residues Rsignifying--independently of one another--hydrogen, alkyl, halogenalkyl,alkoxy, phenyl, halogenphenyl, phenoxy or halogen, and a suitablesolvent; drying the photoresist layer; exposing the photoresist layer inan imaging manner; subjecting the exposed photoresist layer to atemperature treatment in the range of between 120° and 150° C. for aduration of 100 to 600 seconds; subjecting the thus treated photoresistlayer to liquid silylation; and dry-developing the silylated photoresistlayer in an anisotropic oxygen plasma.
 2. The method as defined by claim1, wherein the hydroxy compound is 2,3,4-trihydroxybenzophenone orbisphenol A.
 3. The method as defined by claim 1, wherein the proportionof the photoresist in terms of the photoactive component is 20 to 40%.4. The method as defined by claim 1, wherein an onium compound is addedto the photoactive component.
 5. The method as defined by claim 1,wherein the liquid silylation takes place with a polar, proticsilylation solution.
 6. The method as defined by claim 5, wherein as asilylation solution, a solution of an aminosiloxane in a mixture ofwater and alcohol is used.
 7. The method as defined by claim 1, whereina polymer is used, whose carboxylic acid anhydride groups are based onmaleic anhydride.
 8. The method as defined by claim 7, wherein aterpolymer of maleic anhydride, cinnamic acid tert.-butylester, andstilbene is used.
 9. The method as defined by claim 1, wherein a polymeris used, whose tert.-butylester groups are based on acrylic acid,methacrylic acid, vinylbenzoic acid, or cinnamic acid-tert.-butylester.10. The method as defined by claim 1, wherein a polymer is used, whosetert.-butoxycarbonyloxy groups are based ontert.-butoxycarbonyloxystyrene or -maleinimide.